Multiple input multiple output (MIMO) communication systems using multiple antennae are gaining commercial acceptance as such systems provide an increased spectral efficiency of point-to-point digital communication systems under certain channel conditions. In MIMO communications, symbols (representing bits) are sent from each antenna, and under some channel conditions, result in an increased bit rate without the large power increase required for single antenna point-to-point methods. Over the past decade researchers have shown that significant increases in capacity, and more efficient power usage, can be realized by using multiple antennas at a transmitter and at a receiver.
Efficient power usage improves the user experience because it directly translates to increased operating times and/or smaller portable power sources. Increased operating times are beneficial in any device that uses a portable power source, such as a battery or a fuel cell. Smaller portable power sources also reduce operating expense. Additionally, designers can produce portable devices, e.g., wireless handsets, laptop computers, etc. with more elegant and compact designs or room for additional electronics and features. Smaller power sources can also be less expensive, which leads to lower-cost electronic devices. MIMO technology has matured and is gradually being incorporated into various standards, such as 802.16 (WiMax) and 802.11n.
However, the efficiency gains seen thus far in practice have not sufficiently approached the maximum theoretical gains. To realize the gains predicted from theory, one of the popular methods used is the Vertical-Bell Labs Layered Space-Time (VBLAST) architectures, in which multiple antennas are used at the transmitter as well as at the receiver to achieve spectral efficiencies of 20-40 bps/Hz. Though methods such as VBLAST can be shown, theoretically, to be capacity achieving under idealized transmission conditions, in practice fixed size constellations are employed, and band limited pulse shaping, such as the raised cosine pulse, is employed to deal with band-limited channels. This leads to inefficiencies, leaving room for improvement.
It would be useful to provide a transmission and reception method that is simple to implement and that can work more efficiently than conventional methods.